Section 24. Accidents and Injuries

Chapter 296. Altitude Illness

Topic: Altitude Illness

Altitude Illness

Altitude illness occurs because of a lack of oxygen at high altitudes.

As altitude increases, the atmospheric pressure decreases, thinning the air so that less oxygen is available. For example, compared with the air at sea level, the air in Denver (about 5,300 feet above sea level) contains 20% less available oxygen; the air in Aspen, Colorado (about 8,000 feet above sea level), about 25% less oxygen; and the air near the top of Mount Everest (more than 29,000 feet above sea level), about 66% less oxygen.

Altitude illness occurs when an oxygen deficiency at high altitudes causes fluid in the blood to leak from the smallest blood vessels (capillaries) into the surrounding tissues, resulting in swelling (edema). The forms of altitude illness differ mainly in their degree of severity and where in the body the fluid accumulates. Mild fluid accumulation in the brain causes acute mountain sickness, whereas more severe fluid accumulation in the brain causes high-altitude cerebral edema. Fluid accumulation in the lungs causes high-altitude pulmonary edema. Fluid accumulation in the hands, feet, and face causes high-altitude edema.

Altitude illness is common in people visiting high altitudes. The severity of the illness depends on how high and how quickly a person ascends. For example, most people who, within a day or two, ascend to above 6,000 feet develop high-altitude edema. Acute mountain sickness develops in 10% of people who ascend too rapidly above 8,000 feet, in 25% of people above 9,000 feet, and in almost 50% of people above 14,000 feet. High-altitude pulmonary edema and high-altitude cerebral edema rarely develop at altitudes below 10,000 feet.

People who normally live at sea level or at very low altitudes are more likely to be affected by altitude illness, as are those who engage in strenuous exertion soon after ascent. People with certain lung diseases (such as chronic obstructive pulmonary disease), heart and blood vessel disorders (such as angina, heart failure, or peripheral vascular disease), or blood disorders (such as sickle cell anemia or hemoglobin S-C disease) may have particular difficulties at high altitudes. Asthma, however, does not seem to be worse at high altitudes. Spending less than a few weeks at altitudes below 10,000 feet does not appear to be dangerous for a pregnant woman or the fetus. Physical fitness has no effect on a person's risk of developing altitude illness. Fewer older people than young people develop altitude illness. People who have had high-altitude pulmonary edema and high-altitude cerebral edema previously are particularly likely to develop those conditions again after ascent.

The body eventually adjusts (acclimatizes) to higher altitudes by increasing respiration and heart activity and by producing more red blood cells to carry oxygen to the tissues. Most people can adjust to altitudes of up to 10,000 feet in a few days. Adjusting to much higher altitudes takes many days or weeks, but some people can eventually carry out normal activities at altitudes above 17,500 feet.

Symptoms and Diagnosis

Acute mountain sickness is a mild form of altitude illness. Symptoms usually develop within 4 to 12 hours of ascent and include headache, light-headedness, and, particularly with exercise, shortness of breath. Loss of appetite and nausea and vomiting may follow, along with fatigue, weakness, and irritability. Some people describe the symptoms as similar to those of a hangover. People who stay overnight at a high altitude may have trouble sleeping. Symptoms usually last 24 to 36 hours. However, acute mountain sickness may progress to more severe forms of altitude illness.

High-altitude edema causes swelling of the hands, the feet, and, on awakening, the face. The swelling causes little discomfort and usually subsides in a few days.

High-altitude pulmonary edema may progress from a mild illness to a life-threatening one within a few hours. Symptoms often develop during the second night after ascent, are worse at night, and can become progressively more severe. Mild symptoms usually include a dry cough and shortness of breath after only mild exertion. Moderate symptoms include shortness of breath at rest; confusion; pink or bloody sputum; low-grade fever; and a bluish tinge to the skin, lips, and nails (cyanosis). Severe symptoms include gasping for breath and making gurgling sounds while breathing.

High-altitude cerebral edema is present in a mild form in other types of altitude illness but may become severe. It causes headache, confusion, walking that is unsteady and uncoordinated (ataxia), and coma. These symptoms may progress rapidly from mild to life-threatening within a few hours.

A doctor diagnoses altitude illness based mainly on the symptoms. In high-altitude pulmonary edema, fluid can sometimes be heard in the lungs through a stethoscope. An x-ray of the chest and measurement of the amount of oxygen in the blood can help confirm the diagnosis.

See the sidebar Other Illnesses That Develop at High Altitudes.

Treatment

People with acute mountain sickness must stop their ascent and rest. They should not ascend to higher altitudes until symptoms disappear. Most people with acute mountain sickness improve within a day or two. Acetazolamide or corticosteroids, such as dexamethasone, may help relieve symptoms. Acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) (see Section 6, Chapter 78) help relieve headache.

If symptoms are more severe, supplemental oxygen should be provided through a face mask. If supplemental oxygen is unavailable, however, or if symptoms persist or worsen despite treatment, the person should descend to a lower altitude, preferably at least 2,500 feet lower.

If high-altitude edema is troublesome, diuretics, such as hydrochlorothiazide, can be helpful. However, the swelling resolves after descent, regardless of treatment.

People with high-altitude pulmonary edema should receive oxygen and, if there is no rapid improvement, descend as soon as possible. However, unnecessary exertion should be avoided, because it increases the body's need for oxygen, thus worsening symptoms of high-altitude pulmonary edema. Therefore, the person should be carried to a lower altitude, if possible, and kept warm. The drug nifedipine may temporarily help by decreasing blood pressure in the arteries to the lungs.

If high-altitude cerebral edema develops, the person should descend as far down and as soon as possible. Supplemental oxygen and dexamethasone should be given.

When prompt descent to a lower altitude is not possible, a hyperbaric bag can be used. This device, which consists of a lightweight, portable fabric bag or tent and a manually operated pump, simulates an increase in atmospheric pressure. The person is placed in the bag, which is then tightly sealed. The bag's internal pressure is then increased with the pump. The person remains in the bag for 2 or 3 hours. The hyperbaric bag is as beneficial as supplemental oxygen, which often is not available when mountain climbing.

Prevention

The best way to prevent altitude illness is to ascend slowly, taking 2 days to reach 8,000 feet and another day for each 1,000 to 2,000 additional feet. The altitude at which a person sleeps is more important than the maximum height reached during the day. The pace of ascent should be slowed if symptoms of altitude illness develop.

Acetazolamide taken at the start of the ascent can prevent altitude illness. If taken after the illness has begun, acetazolamide may help lessen symptoms. Acetazolamide should be continued for a few days after ascent. Some doctors believe that dexamethasone can also prevent altitude illness and lessen its symptoms. Ginkgo, a medicinal herb, has proved to be moderately effective in preventing altitude illness. If a person has had previous episodes of high-altitude pulmonary edema, nifedipine, given at the start of ascent, may prevent a recurrence.

Avoiding strenuous exertion for a day or two after arrival may prevent altitude illness, as may eating frequent, small high-carbohydrate meals instead of fewer large meals, and drinking at least 4 quarts of noncaffeinated fluids per day. Alcohol and sedatives, which can cause symptoms similar to acute mountain sickness, should be avoided.

Athletes residing at sea level can take certain steps to prepare for competitions held at high altitudes. For brief, high-intensity competitions such as sprints or jumps, for example, performance is best if the person arrives less than 1 day before the event. For endurance competitions, performance is best if for several weeks beforehand the person trains at low altitudes but sleeps at high altitudes.